U.S. patent application number 10/415338 was filed with the patent office on 2004-02-05 for paper coating slip containing n-vinyl formamide.
Invention is credited to Blum, Thierry, Dirks, Bernd, Franzel, Stefan, Linhart, Friedrich, Mahr, Norbert, Ullrich, Heinrich, Wendker, Martin.
Application Number | 20040020615 10/415338 |
Document ID | / |
Family ID | 7662723 |
Filed Date | 2004-02-05 |
United States Patent
Application |
20040020615 |
Kind Code |
A1 |
Linhart, Friedrich ; et
al. |
February 5, 2004 |
Paper coating slip containing n-vinyl formamide
Abstract
Paper coating slips whose additives comprise addition polymers
or copolymers containing N-vinylformamide in (co)polymerized form,
and their use.
Inventors: |
Linhart, Friedrich;
(Heidelberg, DE) ; Dirks, Bernd; (Hebheim, DE)
; Ullrich, Heinrich; (Freinsheim, DE) ; Blum,
Thierry; (Neustadt, DE) ; Mahr, Norbert;
(Limburgerhof, DE) ; Franzel, Stefan; (Mannheim,
DE) ; Wendker, Martin; (Worms, DE) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
7662723 |
Appl. No.: |
10/415338 |
Filed: |
May 2, 2003 |
PCT Filed: |
November 2, 2001 |
PCT NO: |
PCT/EP01/12685 |
Current U.S.
Class: |
162/135 |
Current CPC
Class: |
D21H 19/58 20130101 |
Class at
Publication: |
162/135 |
International
Class: |
D21H 019/36 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 9, 2000 |
DE |
100 55 592.6 |
Claims
1. The use of an addition polymer or copolymer containing
N-vinylformamide in (co)polymerized form for activating optical
brighteners in paper coating slips.
2. The use as claimed in claim 1, wherein further to the
N-vinylformamide polymer or copolymer the paper coating slip
comprises an optical brightener, at least one white pigment and at
least one binder.
3. The use as claimed in claim 1 or 2, wherein the copolymer
additionally contains at least one water-soluble cationic monomer
in copolymerized form.
4. The use as claimed in any of claims 1 to 3, wherein the
copolymer further contains acrylic acid or methacrylic acid and/or
their salts or mixtures thereof in copolymerized form.
5. The use as claimed in any of claims 1 to 4, wherein the
copolymer further contains N-vinylpyrrolidone in copolymerized
form.
6. The use as claimed in any of claims 1 to 5, wherein the
copolymer further contains at least one additional water-soluble
vinyl monomer in copolymerized form.
7. The use as claimed in any of claims 1 to 6, wherein the
N-vinylformamide present in (co)polymerized form in the addition
polymer or copolymer has undergone partial cleavage.
8. A paper coating slip comprising at least one binder, at least
one white pigment, an optical brightener, and an addition polymer
or copolymer as set forth in any of claims 1 to 6.
9. A paper coating slip as claimed in claim 8, wherein the
copolymer is a cationic copolymer.
10. A paper coating slip as claimed in claim 8 or 9, wherein the
addition polymer or copolymer is composed of: from 1 to 100 parts
by weight of n-vinylformamide from 0 to 10 parts by weight of
water-soluble cationic monomer from 0 to 30 parts by weight of
acrylic acid, methacrylic acid, salts thereof or mixtures of these
from 0 to 90 parts by weight of an additional water-soluble vinyl
monomer.
11. A paper coating slip as claimed in any of claims 8 to 10,
wherein the addition polymer or copolymer is present in amounts of
from 0.2 to 10 parts by weight per 100 parts by weight of
pigment.
12. Paper coated with a slip as claimed in any of claims 8 to
11.
13. The use of paper as claimed in claim 12 in a printing process.
Description
[0001] The invention relates to novel paper coating slips. The
invention further relates to the use of paper coating slips and to
papers coated with said slips.
[0002] Paper coating slips consist essentially of a pigment
(usually white), a polymeric binder, and additives which exert the
desired influence over Theological properties of the slip and
surface properties of the coated paper. Such additives are
frequently also referred to as cobinders. The function of the
binder is to fix the pigments to the paper and ensure cohesion
within the coating obtained.
[0003] Slip coating gives base papers a smooth, uniformly white
surface. The slips also enhance the printability of the paper.
[0004] The coating of paper with slips is nowadays well known; see,
for example, "The Essential Guide to Aqueous Coating of Paper and
Board", T. W. R. Dean (ed.), published by the Paper Industry
Technical Association (PITA), 1997.
[0005] One of the most important objectives of the slip coating of
paper is to increase the whiteness of the paper. At the same time,
however, the surface of the paper must be sufficiently stable that
it is not damaged during printing and that the printed image is not
impaired.
[0006] A host of different measures may be taken to increase the
whiteness of the coated paper. These measures include, for example,
the use of a base paper of very high whiteness, which in turn can
be obtained by using very white starting materials. Another measure
is to select very white pigments for the paper coating slip.
[0007] These measures alone, however, are in the majority of cases
unable to meet the modern-day requirements of users regarding the
whiteness of the paper. It is for this reason that products known
as whiteners (fluorescent or phosphorescent dyes) or optical
brighteners are added to the coating slip. The brighteners are
dyelike fluorescent dyes which absorb the shortwave ultraviolet
light that is invisible to the human eye and emit it as longer-wave
blue light, giving the human eye the impression of a higher
whiteness, so that the whiteness is increased.
[0008] The use of the optical brighteners, however, only results in
the desired outcome if the brighteners are present in an optimum
structure, conformation, and distribution in the finished paper
coating. To achieve this, polymeric compounds, which intensify the
effect of the optical brightener and are referred to as activators
or carriers, are added to the slip. An important function of the
cobinders--mentioned at the outset--in colored coating slips is
their brightener-activating effect. Suitable cobinders may include
water-soluble polymers, e.g., polyvinyl alcohol,
carboxymethylcellulose, anionic or nonionic degraded starches,
casein, soy protein, and water-soluble styrene-acrylate copolymers
(see, for example, K. P. Kreutzer, Grundprozesse der
Papiererzeugung 2: Grenzflchenvorgnge beim Einsatz chemischer
Hilfsmittel, H. -G. Volkel and R. Grenz (editors), PTS Munich,
2000, PTS manuscript: PTS-GPE--SE 2031-2).
[0009] However, it is not possible with every water-soluble polymer
to activate the optical brightener; for example, with certain
polysaccharides, e.g., dextran, or with anionic polyacrylamides, it
is not possible to activate the optical brightener. On the
contrary, it has long been known that water-soluble polymers
containing cationic groups, especially amino or ammonium groups,
such as polyamine/epichlorohydrin or polyamidoamine/epichlorohydrin
resins, polyamines or polyethyleneimines, for example, not only do
not boost the whitener but in fact cause its deactivation, so that
the brightening is extinguished (K. P. Kreutzer, loc. cit., page
8-22).
[0010] DE-A 197 27 503 discloses paper coating slips which comprise
binders containing N-vinylcarboxamide units. The activation of
optical brighteners by additives, however, is not described.
[0011] It is an object of the present invention to provide paper
coating slips having improved properties or leading to an
improvement in the coated paper.
[0012] We have found that this object is achieved by the use of
paper coating slips having improved properties, these slips
including among their additives addition polymers or copolymers
containing N-vinylformamide (formula I) in (co)polymerized form.
1
[0013] In accordance with the invention it is possible as additives
(cobinders) to use addition polymers or copolymers, referred to
hereinbelow as (co)polymers, which consist of N-vinylformamide and,
respectively, contain N-vinylformamide and also anionic, cationic
and/or nonionic monomers in copolymerized form. Moreover, before
their use in a paper coating slip of the invention, the polymers or
copolymers may be subjected to a cleavage operation in which the
carboxylic groups (formyl groups) are partially eliminated.
[0014] It is surprising that the addition of water-soluble
(co)polymers of vinylformamide brings about extraordinarily great
activation of the optical brighteners in paper coating slips. Even
more surprising and entirely unexpected, however, is that cationic
copolymers of vinylformamide--in contrast to what is stated by K.
P. Kreutzer, loc. cit., page 8-22--are likewise suitable as
carriers for optical brighteners and indeed boost their activity
even more than the nonionic polyvinylformamides. The activation of
the whiteners in paper coating slips by (co)polymers of
vinylformamide, in accordance with the invention, is much greater
than the activity of other cobinders in this respect. In addition
to their brightener-activating effect, the (co)polymers
incorporated into the paper coating slips possess the property of
raising the dry pick resistance and wet pick resistance of the
coated paper, and do so to a greater extent than do other
cobinders. Furthermore, it has surprisingly been found that papers
coated with the slips of the invention produce a higher print gloss
than papers coated with slips comprising prior art cobinders.
[0015] The preparation of the polymers of N-vinylformamide which
may be used for the coating slips of the invention has been known
for a long time (see, for example, EP-B1 71 050, corresponding to
U.S. Pat. No. 4,421,602).
[0016] Cationic copolymers containing N-vinylformamide in
copolymerized form may also be used in accordance with the
invention.
[0017] The preparation of cationic copolymers of N-vinylformamide
and a water-soluble basic monomer, such as
N-trialkylammoniumalkylacrylamides,
N-trialkylammoniumalkylmethacrylamides and/or
diallyldialkylammonium salts, for example, and their use as
flocculants and dewatering aids for the treatment of wastewaters
and sludges, are described in EP-B1 464 043 (corresponding to U.S.
Pat. No. 5,225,088).
[0018] For example, as a water-soluble cationic monomer,
diallyldimethylammonium chloride, diallyldiethylammonium
methosulfate, N-(2-trimethylammonium)ethylacrylamide methosulfate
or N-2-(ethyldimethylammonium)ethylmethacrylamide ethosulfate or
mixtures thereof may be copolymerized with N-vinylformamide as
described in EP-B1 464 043, to give cationic copolymers suitable
for use in the colored paper coating slips of the invention.
[0019] It is of course also possible, for the coating slips of the
invention, to use cleaved vinylformamides (see below) in which the
liberated, polymer-bound amino functions form an ammonium formate
with the eliminated formic acid.
[0020] In addition, the preparation of copolymers of
N-vinylformamide and monoethylenically unsaturated carboxylic acids
having from 3 to 8 carbon atoms and/or their alkali metal, alkaline
earth metal or ammonium salts, such as acrylic acid or methacrylic
acid, for example, and also, if desired, other ethylenically
unsaturated, copolymerizable compounds, and their use as additives
to the paper pulp for the purpose of increasing the dewatering rate
and the retention in paper making, and also the dry and wet
strength of the paper, are known from DE-A1 42 41 117
(corresponding to U.S. Pat. No. 5,630,907) and lead to anionic
copolymers which may likewise be used in accordance with the
invention for coating slips.
[0021] Examples of suitable monomers of monoethylenically
unsaturated carboxylic acids having from 3 to 8 carbon atoms, and
of the water-soluble salts of these monomers, include the
following: acrylic acid, methacrylic acid, dimethylacrylic acid,
ethacrylic acid, maleic acid, citraconic acid, methylenemalonic
acid, allylacetic acid, vinylacetic acid, crotonic acid, fumaric
acid, mesaconic acid, and itaconic acid. From this group of
monomers it is preferred to use acrylic acid, methacrylic acid,
maleic acid or else mixtures of said carboxylic acids, especially
mixtures of acrylic acid and maleic acid or of acrylic acid and
methacrylic acid. These monomers or mixtures thereof may be used
either in the form of the free carboxylic acids or in partly or
fully neutralized form for the copolymerization.
[0022] The weight ratio of vinylformamide to monoethylenically
unsaturated carboxylic acid having from 3 to 8 carbon atoms and/or
alkali metal, alkaline earth metal or ammonium salts thereof in the
monomer mixture may range between 100:0 and 70:30, preferred weight
ratios being between 100:0 and 80:20, and particularly preferred
weight ratios being between 100:0 and 90:10.
[0023] Additionally, nonionic copolymers of N-vinylformamide with
further water-soluble vinyl monomers may boost the activity of the
optical brightener in the paper coating slips of the invention.
Further water-soluble vinyl monomers suitable for this purpose
include N-vinylpyrrolidone and other N-vinyllactams, such as
N-vinylcaprolactam, and also N-vinyl-N-alkylcarboxamides or
N-vinylcarboxamides, such as N-vinylacetamide,
N-vinyl-N-methylformamide, and N-vinyl-N-methylacetamid- e, for
example. It is also possible to use mixtures of these.
[0024] A preferred monomer is N-vinylpyrrolidone.
[0025] The composition of the (co)polymers is generally as
follows:
[0026] N-Vinylformamide:
[0027] 1-100 parts by weight, preferably 2-80, with particular
preference 5-80
[0028] Water-soluble cationic monomer:
[0029] 0-10 parts by weight, preferably 0.5-8, with particular
preference 1-5
[0030] Acrylic acid or methacrylic acid and/or their salts or
mixtures thereof:
[0031] 0-30 parts by weight, preferably 1-20, with particular
preference 2-10
[0032] Further water-soluble vinyl monomer:
[0033] 0-90 parts by weight, preferably 0.5-80, with particular
preference 5-50
[0034] A method frequently used, but not the only one, for
preparing the abovementioned (co)polymers is that of free-radical
(co)polymerization in a solvent or diluent.
[0035] The free-radical (co)polymerization of such monomers takes
place, for example, in aqueous solution in the presence of
polymerization initiators which break down into free radicals under
polymerization conditions. The (co)polymerization may be performed
within a wide temperature range, where-appropriate at
subatmospheric or superatmospheric pressure, generally at
temperatures up to 100.degree. C. The pH of the reaction mixture is
commonly adjusted so as to be within the range from 4 to 10.
[0036] The (co)polymerization may also, however, be conducted in
other ways known per se to the skilled worker, for example, as a
solution, precipitation, water-in-oil emulsion or inverse
suspension polymerization. Solution polymerization is
preferred.
[0037] The N-vinylformamide is (co)polymerized using free-radical
polymerization initiators, examples being azo compounds that break
down into free radicals, such as 2,2'-azobis(isobutyronitrile),
2,2'-azobis(2-amidinopropane) hydrochloride or
4,4'-azobis(4'-cyanopentan- oic acid).
[0038] Said compounds are usually used in the form of aqueous
solutions, the lower concentration being determined by the amount
of water that is acceptable in the *(co)polymerization and the
upper concentration being determined by the solubility of the
respective compound in water. In general, the concentration is from
0.1 to 30% by weight, preferably from 0.5 to 20% by weight, with
particular preference from 1.0 to 10% by weight, based on the
solution.
[0039] The amount of the initiators is generally from 0.1 to 10% by
weight, preferably from 0.5 to 5% by weight, based on the monomers
to be (co)polymerized. It is also possible to use two or more
different initiators in the (co)polymerization.
[0040] Examples of solvents or diluents used include water,
alcohols, such as methanol, ethanol, n- or iso-propanol, n- or
iso-butanol, or ketones, such as acetone, ethyl methyl ketone,
diethyl ketone or iso-butyl methyl ketone.
[0041] If desired, the (co)polymerization may be conducted in the
presence of polymerization regulators, such as hydroxylammonium
salts, chlorinated hydrocarbons, and thiocompounds, such as
tert-butyl mercaptan, 2-ethylhexyl thioglycolate, mercaptoethynol,
mercaptopropyltrimethoxysila- ne, dodecyl mercaptan, and
tert-dodecyl mercaptan, or alkali metal hypophosphites. In the
(co)polymerization these regulators may be used, for example, in
amounts of from 0 to 0.8 part by weight per 100 parts by weight of
the monomers to be (co)polymerized, and have the effect of reducing
the molar mass of the resultant (co)polymer.
[0042] In the case of emulsion polymerization, ionic and/or
nonionic emulsifiers and/or protective colloids or stabilizers are
used as surface-active compounds.
[0043] Depending on the polymerization conditions, the
(co)polymerization produces (co)polymers of varying molecular
weights, the molecular weight being characterized in EP-B1 71 050
and below using the Fikentscher K values (measured in 0.5% strength
by weight aqueous sodium chloride solution at 25.degree. C.).
(Co)polymers having a high K value, of above 80, for example, are
preferably prepared by (co)polymerizating N-vinylformamide in
water. (Co)polymers having a high K value with high molecular
weights are obtained, furthermore, by (co)polymerizing the monomers
in the form of inverse suspension polymerization or by
(co)polymerizing the monomers by the technique of water-in-oil
polymerization, for example.
[0044] In the case of the process of inverse suspension
polymerization and that of water-in-oil polymerization, the oil
phase used comprises saturated hydrocarbons, examples being hexane,
heptane, cyclohexane, and decalin, or aromatic hydrocarbons, such
as benzene, toluene, xylene, and cumene. The ratio of oil phase to
aqueous phase in the case of inverse suspension polymerization is,
for example, from 10:1 to 1:10.
[0045] (Co)polymers having a low K value, of below 80, for example,
are obtained if the (co)polymerization is conducted in the presence
of polymerization regulators or in a solvent that regulates the
(co)polymerization, examples being alcohols, such as methanol,
ethanol, n- or iso-propanol, or ketones, such as acetone, ethyl
methyl ketone, diethyl ketone or iso-butyl methyl ketone.
[0046] K values of low molecular weights and correspondingly low K
values are also obtained by means of the customary methods, i.e.,
use of relatively large amounts of polymerization initiator or of
polymerization regulators, or combinations of said measures.
[0047] The molecular weight of the (co)polymers that can be used in
accordance with the invention is not restricted; however, it should
not be too high, so that the coating slip does not have too high a
viscosity. Preference is given to (co)polymers having K values of
between 10 and 80, with K values between 30 and 70 being
particularly preferred.
[0048] In accordance with the invention, vinylformamide
(co)polymers may be used either in partially or fully cleaved form
or else in uncleaved form. Preference is given to a degree of
hydrolysis of between 0 and 30%, with particular preference between
0 and 20%, and with very particular preference between 0 and 10%.
The nature of the elimination of the formyl group is not
restricted, and elimination may be performed, for example, in the
presence of acid or base; preference is given to cleavage in the
presence of bases, such as sodium hydroxide, potassium hydroxide,
alkaline earth metal hydroxides, ammonia or amines, for example. In
this case, partial hydrolysis of, for example, a copolymer
containing (meth)acrylates and vinylformamides in copolymerized
form may give rise to amphoteric (co)polymers.
[0049] In a particularly simple way, however, cationic copolymers
of vinylformamide are obtained by cleaving homopolymers of
vinylformamide hydrolytically to the desired degree of hydrolysis
using defined amounts of acid or base, as described in EP-B1 071
050. Depending on the pH of the solution, the amino groups which
are formed on the polymer chain are more or less protonated and so
give the polymer a more or less cationic character.
[0050] If it is desired to eliminate the formyl group, this may be
done in water.
[0051] The elimination of the formyl group in the hydrolysis takes
place at temperatures in the range from 20 to 200.degree. C.,
preferably from 40 to 180.degree. C., in the presence or absence of
acids or bases. The hydrolysis is preferably conducted within the
temperature range from 70 to 90.degree. C.
[0052] For the acidic hydrolysis, from about 0.05 to 1.5
equivalents of an acid, such as hydrochloric acid, hydrobromic
acid, phosphoric acid or sulfuric acid, are required per formyl
group equivalent in the poly-N-vinylformamide. The pH for the
acidic hydrolysis is in the range from 2 to 0, preferably from 1 to
0. The hydrolysis proceeds with substantially greater rapidity than
that of (co)polymers of other N-vinylcarboxamides, such as of
N-methyl-N-vinylformamide, for example, and may therefore be
conducted under more gentle conditions, i.e., at lower temperatures
and -without a large excess of acids.
[0053] Furthermore, the hydrolysis of the formyl groups of the
poly-N-vinylformamide may also be carried out in an alkali medium,
in the pH range from 11 to 14, for example. This pH is preferably
set by adding sodium hydroxide or potassium hydroxide solution. It
is, however, also possible to use ammonia, amines and/or alkaline
earth metal bases. From 0.05 to 1.5, preferably from 0.4 to 1.0,
equivalent(s) of a base is (are) used for the alkaline
hydrolysis.
[0054] The cleavage may also be carried out at high temperatures,
for example, above 100.degree. C., preferably from 120 to
180.degree. C., with particular preference from 140 to 160.degree.
C., in the presence of a solvent, e.g., water, without acid or
base. This is preferably done under conditions above the critical
point, using supercritical water, for example.
[0055] In the course of the hydrolysis--i.e., the formyl group is
eliminated from the poly-N-vinylformamide in water in the presence
of acids or bases--the byproduct comprises formic acid and/or salts
of formic acid.
[0056] The resulting solutions may be used without further workup,
or else the hydrolysis and/or solvolysis products may be separated
off.
[0057] For separation, the solutions obtained are treated using ion
exchangers, for example. The residue separated from the hydrolysis
products may then be incorporated into the coating slips.
[0058] The amount of vinylformamide (co)polymers added to the paper
coating slip of the invention is guided by the amount of brightener
in the slip.
[0059] Normally, from 0.2 to 2 parts by weight of optical
brightener per 100 parts by weight of pigment are added to the
coating slip. The amount of (co)polymer added to the coating slip
is normally equal to from 1 to 5 times the amount of the optical
brightener, i.e., from 0.2 to 10 parts by weight, preferably from
0.5 to 8 parts by weight, and with particular preference from 1 to
5 parts by weight.
[0060] The paper coating slips of the invention preferably comprise
at least one optical brightener.
[0061] The coating slips of the invention are processed completely
in analogy to processing of coating slips in accordance with the
prior art, e.g., in accordance with "The Essential Guide to Aqueous
Coating of Paper and Board", T. W. R. Dean (ed.), Published by the
Paper Industry Technical Association (PITA), 1997 or "Ratgeber fur
die Verwendung von BASF-Erzeugnissen in der Papier-und und
Kartonstreicherei", BASF Aktiengesellschaft, D-6700 Ludwigshafen,
Federal Republic of Germany, B 376 d, 09.77.
[0062] Besides the additive of the invention, the paper coating
slips of the invention further comprise at least one white pigment
and at least one binder.
[0063] The paper coating slips may further comprise other
ingredients known to the skilled worker. Suitable examples include
leveling assistants, pigment wetting aids, etc.
[0064] There is no restriction of the optical brighteners that may
be used in connection with the coating slips of the invention. It
is possible to use the commercially customary stilbene derivatives
substituted by up to 6 sulfonic acid groups, an example being
Blankophor.RTM. PSG from Bayer AG, or derivatives thereof, or
4,4'-distyrylbiphenyl derivatives.
[0065] The pigments that may be used in the coating slips of the
invention are likewise not subject to any restriction. For example,
use may be made of satin white (calcium sulfoaluminate), calcium
carbonate in ground or precipitated form, barium sulfate in ground
or precipitated form, kaolin (clay), calcined clay, talc,
silicates, chalk or coating clay, or organic pigments, e.g.,
plastics in particle form.
[0066] Nor is there any restriction on the binders ((co)polymeric
binders) that may be used in the coating slips of the invention.
For example, casein, starch, soy protein, carboxymethylcellulose,
alginate and/or polyvinyl alcohol or dispersions containing acrylic
acid, acrylates, vinyl acetate and/or styrene in copolymerized
form, e.g., (co)polymers of acrylate/styrene, styrene/butadiene or
vinyl acetate, may be used. The paper coating slips may further
comprise, for example, dispersants. Suitable dispersants are
polyanions, for example those of polyphosphoric acids or of
polyacrylic acids (polysalts), which are normally present in
amounts of from 0.1 to 3% by weight, based on the pigment
amount.
[0067] To prepare the paper coating slip, the ingredients are mixed
conventionally, with the (co)polymer being used generally in the
form of a dispersion, suspension or solution.
[0068] The amount of water in the paper coating slip is usually
adjusted to from 25 to 75% by weight, based on the overall paper
coating slip (including water).
[0069] The paper coating slip may be applied by customary
techniques to the papers to be coated (cf. Ullmann's Encyclopdie
der Technischen Chemie, 4th edition, Vol. 17, p. 603 ff).
[0070] If desired, a thickener may be added as well. Suitable
thickeners include free-radically (co)polymerized (co)polymers and
customary organic and inorganic thickeners such as
hydroxymethylcellulose or bentonite.
[0071] In the majority of cases, the paper coating slips are
aqueous slips. The water content may be adjusted in accordance with
the desired viscosity or flow properties.
[0072] To prepare the paper coating slip, the ingredients may be
mixed in a known manner. The paper coating slips of the invention
are suitable for coating, for example, paper or board. The paper
coating slip may then be applied to the papers or board by
conventional techniques.
[0073] The papers or boards coated with the paper coating slips of
the invention may be printed in customary processes, e.g., offset,
letterpress or gravure printing processes.
[0074] The examples below are intended to illustrate the properties
of the paper coating slips of the invention but without restricting
the invention to these particular coating slips.
[0075] In this specification, parts are by weight unless otherwise
specified.
EXAMPLE 1
[0076] A coating slip was prepared having the following
composition:
[0077] 70 parts of calcium carbonate (Hydrocarb.RTM. 90,
Pluss-Staufer AG)
[0078] 30 parts of kaolin (Amazon 88, Kaolin International)
[0079] 8 parts of styrene-butadiene latex (Styronal.RTM. 610, BASF
Aktiengesellschaft)
[0080] 0.5 part of optical brightener (Blankophor.RTM. PSG, Bayer
AG)
[0081] and as cobinder:
[0082] 0.5 part of carboxymethylcellulose (CMC 7L2T, Hercules GmbH)
or
[0083] 0.5 part of polyvinylformamide (PVFA) having a K value of 51
and a degree of hydrolysis as specified in table 1.
[0084] The coating slips, with a solids content of 68.1% by weight,
were applied at a coat weight of 16 g/m.sup.2 to chemical paper
with a basis weight of 70 g/m.sup.2 and the paper was then
glazed.
[0085] The brightening of the paper was determined in accordance
with DIN 53 145, part 2.
[0086] The CIE whiteness of the paper was measured in accordance
with ISO 2469.
[0087] When determining the dry pick resistance in accordance with
the IGT method using the Lorilleux ink 3808 at 85 cm/s, the ink
density was determined using the Gretag densitometer.
[0088] When determining the wet pick resistance in accordance with
using the test bench instrument using the Lorilleux ink 3804 at 35
cm/s, the ink density was determined using the Gretag
densitometer.
[0089] Additionally, the 75.degree. print gloss of the papers was
measured by the Lehmann method.
[0090] The test results for the coated papers are given in table
1.
1TABLE 1 PVFA PVFA PVFA Degree of Degree of Degree of hydrolysis
hydrolysis hydrolysis Cobinder CMC 7L2T 0% 3% 8.5% Whiteness % 91.0
92.9 93.9 94.1 R 457 with UV Whiteness % 85.9 86.4 87.0 87.1 R 457
without UV Brightening % 5.1 6.5 6.9 7.0 Whiteness % 102.3 109.2
111.4 111.3 CIE IGT dry 0.53 0.94 1.25 1.25 (85 cm/s) Test bench
wet 0.70 1.71 1.81 1.55 (35 cm/s) Print gloss % 69.5 71.8 72.1
76.6
[0091] The coating slips of the invention which comprise a
polyvinylformamide (PVFA) experience greater optical brightening
and possess a higher CIE whiteness than the coating slips which, in
accordance with the prior art, comprise carboxymethylcellulose as
cobinder. It is also evident that polyvinylformamides having
undergone a certain degree of hydrolysis and therefore being
cationic provide greater brightening and CIE whiteness than
nonionic PVFA. Moreover, it can be seen that the coating
compositions that include a polyvinylformamide have much better
properties in terms of both dry and wet pick resistance than those
comprising CMC as cobinder. Finally, the coating slips of the
invention also produce a markedly higher print gloss.
EXAMPLE 2
[0092] A coating slip was prepared having the following
composition:
[0093] 70 parts of calcium carbonate (Hydrocarb 90, Pluss-Staufer
AG)
[0094] 30 parts of kaolin (Amazon 88, Kaolin International)
[0095] 8 parts of styrene-butadiene latex (Styronal.RTM. 615, BASF
Aktiengesellschaft)
[0096] 0.5 part of optical brightener (Blankophor PSG, Bayer
AG)
[0097] The cobinders used were as follows:
[0098] 0.5 part of carboxymethylcellulose (CMC 7L2T, Hercules GmbH)
or
[0099] 0.5 part of polyvinyl alcohol (Mowiol.RTM. 6-98, Clariant
Aktiengesellschaft) or
[0100] 0.5 and
[0101] 1.0 part of polyvinylformamide (PVFA) having a K value of 45
and a degree of hydrolysis of 5%.
[0102] The coating slips were processed as described in example
1.
[0103] The brightening and whiteness of the glazed papers, and the
print gloss, were determined as described in example 1.
[0104] The test results are set out in table 2.
2 TABLE 2 Polyvinyl alcohol Cationic PVFA CMC Mowiol Degree of 7L2T
6-98 hydrolysis 5% Cobinder none 0.5% 0.5% 0.5% 1.0% Whiteness %
89.8 91.2 93.0 94.3 95.0 R 457 with UV Whiteness % 85.0 85.8 86.1
87.0 86.8 R 457 without UV Brightening % 4.8 5.4 6.9 7.3 8.2
Whiteness % 99.3 103.5 111.0 113.1 116.6 CIE Print gloss % 72.6
72.2 70.2 73.8 75.5
[0105] Table 2 reveals that the coating slips of the invention
containing polyvinylformamide produce a higher whiteness and a
greater print gloss than the coating slips that contain other
cobinders.
EXAMPLE 3
[0106] A coating slip was prepared having the following
composition:
[0107] 70 parts of calcium carbonate (Hydrocarb 90, Pluss-Staufer
AG)
[0108] 30 parts of kaolin (Amazon 88, Kaolin International)
[0109] 8 parts of styrene-butadiene latex (Styronal.RTM. PR 8736,
BASF Aktiengesellschaft)
[0110] 0.5 part of optical brightener (Blankophor PSG, Bayer
AG)
[0111] The cobinders used were as follows:
[0112] 1.0 part of carboxymethylcellulose (CMC 7L2T, Hercules GmbH)
or
[0113] 1.0 part of acrylic-based copolymer (Acrosol.RTM. C 50 L,
BASF Aktiengesellschaft) or
[0114] 1.0 part of polyvinylformamides (PVFA) having a K value of
50 and a degrees of hydrolysis of 1% and 5%.
[0115] The coating slips were processed as described in example
1.
[0116] The brightening and whiteness of the glazed papers, and
their dry and wet pick resistances, were determined as described in
example 1.
[0117] The test results are set out in table 3.
3TABLE 3 PVFA PVFA Degree of Degree of Acrosol C hydrolysis
hydrolysis Cobinder CMC 7L2T 50 L 1% 5% Whiteness % 91.9 92.7 93.4
94.3 R 457 with UV Whiteness % 86.2 86.3 86.1 86.5 R 457 without UV
Brightening % 5.7 6.4 7.3 7.8 Whiteness % 105.3 107.8 111.6 113.8
CIE Test bench wet 0.55 0.52 1.44 1.21 (130 cm/s)
[0118] The results set out in table 3 confirm that using the
coating slips of the invention prepared with the additives
described gives rise to papers having higher whiteness and greater
strength than when using coating slips comprising prior art
cobinders.
EXAMPLE 4
[0119] A coating slip was prepared having the following
composition:
[0120] 70 parts of calcium carbonate (Hydrocarb 90, Pluss-Staufer
AG)
[0121] 30 parts of kaolin (Amazon 88, Kaolin International)
[0122] 10 parts of styrene-acrylate latex (Acronal.RTM. S 360 D,
BASF Aktiengesellschaft)
[0123] 0.5 part of carboxymethylcellulose (CMC 7L2T, Hercules GmbH)
as cobinder for all formulas
[0124] 0.5 part of optical brightener (Blankophor PSG, Bayer
AG)
[0125] As an additional cobinder the following were used:
[0126] 0.5 part of carboxymethylcellulose (CMC 7L2T, Hercules GmbH)
or
[0127] 0.5 part of polyvinylformamide (PVFA) having a K value of 69
and a degree of hydrolysis of 1%.
[0128] The coating slips were processed as described in example
1.
[0129] The brightening and whiteness of the glazed papers and their
dry and wet pick resistances were determined as described in
example 1.
[0130] The test results are reproduced in table 4.
4TABLE 4 PVFA K value 69 Degree of hydrolysis Additional cobinder
CMC 7L2T 1% Whiteness R 457 % 94.0 95.8 with UV Whiteness R 457 %
87.4 88.5 without UV Brightening % 6.6 7.3 Whiteness CIE % 110.7
111.6 IGT dry 1.35 1.80 (170 cm/s) Test bench wet 0.78 1.28 (130
cm/s)
[0131] The results in table 4 show that the coating slips of the
invention produce an improvement even when they already contain a
conventional cobinder, the addition of the novel additive making
the quality of the coated paper much higher than when the same
amount of the cobinder already present in the slip is added.
EXAMPLE 5:
[0132] A coating slip was prepared having the following
composition:
5 70 parts of calcium carbonate (Hydrocarb 90, Pluss-Staufer AG) 30
parts of kaolin (Amazon 88, Kaolin International) 10-12 parts (see
table 5) of styrene-butadiene latex (Styronal LD 615, BASF
Aktiengesellschaft) 0.5 part of optical brightener (Blankophor PSG,
Bayer AG)
[0133] Sterocoll.RTM. FD as indicated in table 5.
[0134] The cobinders used were as follows:
[0135] 1.0 part of oxidatively degraded starch (Emox.RTM. TSC,
Emsland-Strke GmbH) or
[0136] 2.0 parts of oxidatively degraded starch (Emox TSC,
Emsland-Strke GmbH) or
[0137] 0.5 part of polyvinylformamide (PVFA) with a K value of 69
and a degree of hydrolysis (DH) of 1% and 5% respectively.
[0138] The coating slips were processed as described in example
1.
[0139] The brightening and whiteness of the glazed papers and their
wet pick resistances were determined as described in example 1.
[0140] The blister resistance was determined by immersing the
papers, coated on both sides, in hot oil (240.degree. C.). The
blistering was assessed with a rating from 1 (no blisters) to 6
(very many blisters).
[0141] The test results are set out in table 5.
6TABLE 5 Parts of 12 11 10 11 11 Styronal LD 615 Parts of 0.30 0.25
0.2 0.5 0.5 Sterocoll FD Cobinder -- Oxid. Oxid. PVFA PVFA (parts)
starch starch DH 1% DH 5% (1.0) (2.0) (0.5) (0.5) Whiteness R %
92.2 92.9 92.6 94.5 93.4 457 with UV Brightening % 4.5 4.8 4.7 6.2
6.4 Whiteness % 100.8 103.2 103.4 108.6 109.4 CIE Test bench wet
1.11 1.32 0.93 1.69 1.21 (135 cm/s) Blistering at 6 3 5 1 2
240.degree. C.
[0142] Table 5 reveals that although degraded starches likewise
increase the whiteness of the paper, they fail to achieve the
effectiveness in this respect of the much smaller amounts of
polyvinylformamides. It is also evident that the papers produced
using polyvinylformamides as cobinders combine an equivalent or
higher wet pick resistance with a substantially reduced blistering
tendency in comparison with the papers produced using starch.
EXAMPLE 6
[0143] A coating slip was prepared having the following
composition:
[0144] 70 parts of calcium carbonate (Hydrocarb 90, Pluss-Staufer
AG)
[0145] 30 parts of kaolin (Amazon 88, Kaolin International)
[0146] 8 parts of styrene-butadiene latex (Styronal D 610, BASF
Aktiengesellschaft)
[0147] 0.5 part of optical brightener (Blankophor PSG, Bayer
AG)
[0148] The following cobinders were used:
[0149] 0.5 part of carboxymethylcellulose (CMC 7L2T, Hercules GmbH)
or
[0150] 0.5 part of a copolymer of vinylformamide and acrylic acid
(VFA/AA) in a ratio of 80:20 with a K value of 38 or
[0151] 0.5 part of a copolymer of vinylformamide and acrylic acid
(VFA/AA) in a ratio of 90:10 with a K value of 43.
[0152] The coating slips were processed as described in example
1.
[0153] The brightening and whiteness of the glazed papers were
determined as described in example 1.
[0154] The test results are recorded in table 6.
7TABLE 6 80:20 VFA/AA 90:10 VFA/AA Cobinder CMC 7L2T copolymer
copolymer Whiteness R 457 % 91.3 91.6 92.4 with UV Whiteness R 457
% 85.9 86.1 86.2 without UV Brightening % 5.1 5.5 6.2 Whiteness CIE
% 102.3 104.6 106.7
[0155] The tests show that even the addition of anionic
polyvinylformamides produces coating slips which give rise to
papers with greater whiteness than coating slips containing prior
art cobinders.
EXAMPLE 7
[0156] A coating slip was prepared having the following
composition:
[0157] 70 parts of calcium carbonate (Omyalite.RTM. 90,
Pluss-Staufer AG)
[0158] 30 parts of kaolin (Amazon 88, Kaolin International)
[0159] 10 parts of styrene-acrylate latex (Acronal S 305 D, BASF
Aktiengesellschaft)
[0160] 0.5 part of optical brightener (Blankophor PSG, Bayer
AG)
[0161] The cobinders used were as follows:
[0162] 2 parts of polyvinyl alcohol (Polyviol.RTM. LL 603,
Wacker-Chemie GmbH) or
[0163] 3.5 parts of oxidatively degraded starch (Emox TSC,
Emsland-Strke GmbH) or
[0164] 2 parts of polyvinylformamide (PVFA) having a K value of 32
and degrees of hydrolysis of 0%, 1% and 5% respectively.
[0165] The coating slips were processed as described in example
1.
[0166] The brightening and whiteness of the glazed papers and their
dry and wet pick resistances, were determined as described in
example 1.
[0167] The test results are set out in table 7.
8TABLE 7 PVFA PVFA PVFA degree of Degree of Degree of Polyvinyl
Oxid. hydrolysis hydrolysis hydrolysis Cobinder alcohol Starch 0%
1% 5% Whiteness % 94.0 92.2 95.2 96.0 95.6 R 457 with UV Whiteness
% 86.4 86.1 86.8 87.4 87.2 R 457 without UV Brighten- % 7.6 6.1 8.4
8.6 8.4 ing
[0168] Table 7 shows that even the addition of nonionic and
cationic polyvinylformamides having a low molecular weight (K
value) to coating slips produces papers having greater optical
brightening than can be achieved by adding prior art cobinders.
* * * * *